Valves of this type are usually available through commercial channels. Since the predominant control pressure applied to the appliance connection acts on both sides of the valve piston in such directly controlled pressure limiting valves by means of the associated actuating device, and since the control pressure accordingly does not exert its effect on the valve piston, the same valve piston diameter may be advantageously used for different pressure stages involved. In other words, even at higher pressure stages, no especially small valve piston diameter need be chosen to keep the piston forces which occur within limits. Such valves with valve pistons of sufficiently large diameter may be designed for relatively high rated volume flows.
Although high piston forces are not applied to the actuating system in a valve of this design, the flow forces occurring during operation on the control edges of the valve piston are transmitted undiminished to the actuating system. This disadvantage results in the operating characteristic of the valve having a relatively sharply rising curve in the pressure restriction function and a sharply dropping curve in the pressure reduction function. This falling characteristic occurs in particular in the case of pump pressures which are very high in comparison to the control pressure, since the sharp drop in pressure causes especially high flow forces to be applied to the respective control edge of the valve piston, reducing the opening stroke of the piston.